Lyme Regis case study: The Preliminary Studies
		The Cobb Introduction Phase 1: Cobb Gate to Church Cliff Phases II & III: Cobb Gate to the harbour Phase IV: East Cliff Monmouth Beach
		The structure
Other pages Lyme Regis homepage Preliminary Studies Summary of Problems Immediate Action Outline Solutions		Principal Findings 1. The Cobb is a Grade 1 Listed Structure, of national historical importance, and is the oldest working breakwater of its type in the country. 2. The structure has undergone many phases of repair and rebuild since the 13th century. 3. Much of the High Wall, from the Causeway to the end of the Southern Arm, and including the Raised Walkway, was constructed between c1793 and c1825, probably with a high quality hearting of large-block coursed masonry bedded in mortar. 4. There is a 60m length of the High Wall at the junction with the Landing Quay which is considerably older and has a hearting of poorer quality. 5. The Low Walkway and the present-day Causeway were built as add-ons in 1834 and 1857 respectively with a hearting of beach shingle. 6. There are areas of extensive open joints low down on the exterior face of the High Wall and continual undermining of the mudstone foundation. These present considerable maintenance problems due to difficulty of access, particularly at Monmouth Beach where the foundation is usually concealed by beach material. 7. There is a bulging of the harbour wall along about 80m of its length and settlement of the adjacent concrete decking on the Low Walkway. These features have existed for many years. 8. There are small voids immediately below the decking of the Low Walkway. 9. The decking of the Low Walkway and the Causeway has continued to deteriorate in recent years, exacerbated by trafficking by motor vehicles and by scouring from seawater and shingle during storms. 10. The Low Walkway acts as a buttress to the High Wall and Raised Walkway and its integrity may therefore be significant for the stability of the Cobb structure as a whole.
		Problem 1. The lower parts of the High Wall are deteriorating and are difficult to maintain. The most problematic sections are: (a) The old section of the High Wall and (b) the section of the High Wall adjacent to Monmouth Beach. 2. The Low Walkway is vulnerable to scouring by seawater and shingle overtopping the High Wall during storms.
		Consequences 1. The Cobb will fail by progressive collapse of the external masonry and hearting due to erosion of jointing material or undermining of the mudstone ledges on which the structure is founded. This will lead to the loss of the harbour and flooding and erosion of nearby properties. 2. Excessive souring of the surface of the Low Walkway will lead quickly to the destruction of the Walkway 3. There is a possibility that the Cobb could fail by the High Wall sliding on its mudstone foundation under extreme wave conditions following the destruction of the Low Walkway.
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